1. Field of the Invention
This invention relates to an image sensing apparatus using a flash device in combination with an image sensor such as a camera tube, a CCD or the like.
2. Description of the Prior Art
The conventional electric flash device for a camera starts flashing by ionizing a gas within a flash discharge tube with a trigger voltage of several thousand volts and several hundred KHz. Meanwhile, the image sensor of an electronic camera and a signal processing circuit following it are required to process a weak signal high frequency. This point represents a fundamental difference of the camera of the above-stated kind from the conventional camera which uses a silver halide film. The high voltage, high frequency trigger signal, therefore, causes noises and erroneous actions to a great extent. Furthermore, in order to give effective illumination, the flash device of the kind generally used for a camera must have capacitor a large capacity quickly charged with a sufficient amount of energy for flashing. That requires a switching action to be performed on a large current within a booster circuit for charging. Then, the switching action produces a very large amount of noise.
The present invention is directed to the elimination of the above-stated inconveniences which result from the use of conventional electric flash devices for an electronic camera. It is therefore an object of the invention to provide an image sensing apparatus which is free from the adverse noise resulting from a trigger signal.
It is another object of the invention to provide an image sensing apparatus which is of the kind to be used together with an illumination device such as a flash device and which is capable of preventing picture quality from being eroded by noise produced during charging of the illumination device with the noises mixing in the outputs of a signal processing circuit, a recording circuit, etc.
These and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.